The present invention relates to a gas driven rotation motor, a tool provided with a gas driven rotation motor and a method for regulating the rotation speed of a gas driven rotation motor.
Gas driven rotation motors, or pneumatic motors, are used in machines with rotating tools such as grinding machines, milling machines, drilling machines, etc. In particular, gas driven rotation motors are used in portable power tools and hand held power tools for a number of different applications including construction, manufacturing, dental machines, artists' works etc.
Vane motors and turbine motors are the most common types of gas driven or pneumatic motors. In the turbine motor the rotation speed is considerably higher than in the vane motor. For both types of motors, speed governors are used to regulate the inflow of air, or other gas if such is used, to the motor and thereby limiting to a maximum the rotation speed at idle running. It is particularly important to be able to control the rotation speed (rpm) of tools with high speed turbine motors, for instance in grinding machines because in grinder applications there is a risk for explosion or centrifugal disintegration of the grinding disc should the motor speed exceed a certain safety level at idle running. Breaking up of the grinding tool in this way would be very hazardous for the operator and other people and equipment in the vicinity of the tool in operation. The purpose of the speed governor is to restrict the air inlet flow for the rotor when the motor speed approaches the safety level, but to let through an unrestricted air flow at the normal working speed of the motor. There is a particular problem to have mechanical speed governors operate properly at high speed motors like turbines. Usually, also some kind of overspeed safety or shutoff device is provided.
Centrifugally operated and rotatably driven speed governors or regulators are previously known. In U.S. Pat. No. 6,179,552 is disclosed a speed governor (“speed control unit”) for a turbine motor. The speed governor includes two or more flyweight members mounted in a bore in the rotor. The overspeed safety device includes an elastically deformable spring element arranged to be radially bent by centrifugal action to hit and release a trip element in order to thereby free an airflow restricting element.
Another type of centrifugally driven speed governor has been in use since the 1960's, a so called ball speed governor as disclosed in DE1875308U. This speed governor includes weights in the form of balls that roll in a conical seat. Such a speed governor is also illustrated in FIG. 1 and FIG. 2, having reference number 4. This speed governor is normally used with vane type rotation motors having a fairly low rotation speed. In order to use such a speed governor with a turbine motor, some type of gear arrangement must be used between the rotor and the speed governor in order to reduce the rotation speed to a level at which the speed governor is operable.
The purpose of the present invention is to provide a tool having a gas driven rotation motor that can easily be connected to a centrifugally driven speed governor, for example such speed governors that already exists on the market. A further object of the invention is to provide a safe-failure design for this critical component.